Disc drive memory systems are being utilized in progressively more environments besides traditional stationary computing environments. Recently, these memory systems are incorporated into devices that are operated in mobile environments including digital cameras, digital video cameras, video game consoles and personal music players, in addition to portable computers. These mobile devices are frequently subjected to large magnitudes of mechanical shock as a result of handling. As such, performance and design needs have intensified including improved resistance to a shock event, improved robustness and reduced power consumption.
Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. At least one disc is rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is typically used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the stator. One type of motor has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the sleeve, while maintaining alignment of the spindle to the shaft. The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information.
A demand exists for increased storage capacity and smaller disc drives, which has led to the design of higher recording areal density such that the read/write heads are placed increasingly closer to the disc surface. Because rotational accuracy is critical, disc drives currently utilize a spindle motor having fluid dynamic bearings (FDB) between a shaft and sleeve to support a hub and the disc for rotation. In a hydrodynamic bearing, a lubricating fluid provides a bearing surface between a fixed member and a rotating member of the disc drive. Hydrodynamic bearings, however, suffer from sensitivity to external loads or mechanical shock. Fluid can in some cases be jarred out of the bearing by shock events.
Lubricant evaporation can limit the life of a hydrodynamic bearing motor. A sufficient amount of lubricant such as oil must be maintained to offset evaporation losses. The evaporation rate is further accelerated when special low viscosity oils are used to reduce power. The lower viscosity oils generally have a higher rate of evaporation. If a shock event occurs with a motor having an insufficient volume of lubricant, rotating surfaces may come in direct contact with stationary portions. Contact of the rotating surfaces can increase generated acoustic noise and motor run current. The dry surface-to-surface contact may also lead to particle generation or gall and lock-up of the motor during contact. Particle generation and contamination of the bearing fluid may also result in reduced performance or failure of the spindle motor or disc drive components.